by Gill Jennings

Created on: April 03, 2009

What is "bleeding" a radiator system?

Bleeding is the removal of air from each radiator in the system. All radiator systems gradually accrue a build-up of air, which gets in with the water, and prevents the water in the system from circulating properly.

Bleeding your radiators is something that should be done on a regular basis. The frequency depends on your system but it is very easy to check whether it needs bleeding. Simply turn on the central heating, allow the system to get going, then visit each radiator in turn. Feel the radiator at the top and the bottom. If the radiators are all fully warm, your system is fine and should be left alone. If any of the radiators are cool or even cold at the top, they need bleeding. Do check that all the lower valves are open, i.e. the radiators are switched on!

To bleed most radiator systems, the first thing you must do is turn off the system, and wait for it to cool down. Don't run the risk of scalding yourself.

Next, you need a radiator key. This is usually made of brass, and is a short cylinder with a square "bore" (the hole up the middle) and a cross-bar at the other end to facilitate turning. This key should have been provided when your system was installed, but if you no longer have one they are easily obtainable from hardware stores. The other thing you need is a supply of rags or paper towels, as a small amount of water always escapes when you bleed a radiator. Radiator water is often quite dirty, so you need to prevent it from getting onto your walls or carpets.

The air in radiators rises above the water, so there is likely to be more air in the radiators at the top of the house. For this reason, bleed the radiators in the lower rooms first and work your way upwards.

Now locate your first "bleed valve". This is a small valve at one end of the top of the radiator. It has a square protrusion in the centre, this is where your bleed key fits. Place your bleed key onto the bleed valve, and hold your rag or paper towel under & around the valve. Turn the key very gently, just a quarter turn, and listen for the hiss of escaping air. It may be necessary to turn the key a little further, but only a little, no more than a half turn. Keep the key in the valve, ready to close it quickly. As soon as the hissing stops & you hear the bubbling sound of water coming through the bleed valve, turn the key back to close the valve. Radiator systems are usually pressurized, and you may be taken aback by the speed at which the water comes through.

Repeat this process with each radiator in turn. Finally, top up your radiator system with fresh water (your instruction manual will tell you how to do this). This is a very important step to remember, as your system will not work correctly unless there is sufficient water in it.

Turn your system back on, and enjoy the renewed warmth!

Notes:

1 If your heating system had a large amount of air in it, it is probably a good idea to repeat the process after about a week.

2 Some modern radiators do not require the use of a bleed key, as the valves can be turned with a flat screwdriver. The process remains the same.

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